The present disclosure relates to a method for adjusting a writing strategy for recording (exposing) with regard to a disc master (master strategy adjustment method). In addition, the present disclosure relates to a method of manufacturing an optical disc recording medium which is created based on the disc master.
There is recording of information using a combination of pits and lands in, for example, an optical disc recording medium such as a CD (Compact Disc), a DVD (Digital Versatile Disc), or a BD (Blu-ray Disc: registered trademark) as a so-called ROM (Read Only Memory) type. That is, there is recording of information using a formation pattern with a concave section as a pit and a convex section as land.
In manufacturing of a ROM type optical disc recording mediums such as this, first, information recording is performed by a laser light illumination being performed with regard to an optical disc master where a photo-sensitive layer is formed. Then, after a master where recording is completed where a pit has been formed is created by a development process with regard to the optical disc master where a recording process has been carried out in this manner and a stamper is created which transfers a pit pattern (thus, recording information) which is formed on the master where recording is completed, the optical disc recording medium is manufactured by a substrate being formed with the recording information being reproduced by injection molding or the like using the stamper and by depositing or the like of a reflecting film with regard to the substrate.
In a method for manufacturing an optical disc recording medium such as this, in recent years, a PTM (Phase Transition Mastering) method has been adopted in the recording process (mastering process) in order to support higher recording density in optical disc recording mediums. It is referred to as so-called thermography.
In the PTM method, an inorganic resist is used as a photoresist which configures a photo-sensitive layer. A semiconductor laser is used as a recording laser.
Here, in the method in the related art where the PTM method is not adopted, an organic resist is used as the photo-sensitive layer. In this case, a portion which is exposed using a laser remains as a pit since exposure of the photoresist is so-called optical recording. That is, the laser spot diameter as it is has an effect on pit width.
On the other hand, in the PTM method, characteristics of an inorganic resist are changed (that is, chemical characteristics are changed) by heat being applied in accompaniment to irradiation of laser light and a recording mark is formed. The inorganic resist which is used in the PMT method exhibits remarkable changes in chemical properties at a portion where heat is concentrated, and the size of a groove which is formed is not directly affected by the laser spot diameter. That is, due to this point, it is possible to perform more precise groove formations in the PTM method than in the method in the related art.
However, it is necessary to set an appropriate writing strategy even in a case where laser illumination is performed according to a recording signal in order to manufacture the disc master. For example, with regard to the disc master for manufacturing an optical disc with a bit length as 2 T to 9 T (where T is a channel clock), exposure which corresponds to 2 T to 9 T pits is performed using laser illumination during the recording of the disc master. At this time, for each bit length of 2 T to 9 T, it is possible to achieve an improvement in product quality of pit rows of the optical disc which is eventually manufactured by appropriately adjusting a strategy pattern (recording drive waveform which is applied to a laser light emission section).
At this time, in a case where the PTM method is adopted in the recording process of the master, strategy adjustment during master recording in this manner is able to be executed without carrying out a development process (forming process of the pit) with regard to the master.
That is, as is shown in Japanese Unexamined Patent Application Publication No. 2009-64542, in a case where the PTM method is adopted, it is possible to read out a signal, which is recorded in the formation portion and other portions, using laser light illumination using reproduction power without a concave section being formed as a pit due to the development process since there is deforming (warping) in the portion where laser light is illuminated in the inorganic resist. That is, it is possible to perform measurement of an evaluation value according to strategy adjustment based on the signal which is read out in this manner.
It is possible to considerably improve the operational efficiency since it is sufficient if the processes after the development process are not performed in the measurement of the evaluation value for strategy adjustment.
However, it is necessary to improve the signal quality of the optical disc as the final product, not the master.
Normally, the evaluation value which is measured from the optical disc may not necessarily become an optimal value even if the evaluation value which is measured from the master is adjusted to be an optimal value. This is because there may be differences in the bit length which is formed on the master and the optical disc due to various causes in the processes since there are many processes such as stamper forming, substrate forming, and depositing from the forming of the master to the creation of the optical disc.
Due to this, in a case where the efficiency of the strategy adjustment operation is achieved due to the method described in Japanese Unexamined Patent Application Publication No. 2009-64542 described above (that is, the processes from the development process to the forming of the optical disc are omitted), a value, where the evaluation value which is measured from the optical disc is set to be an optimal value as the target value of the evaluation value which is used in strategy adjustment and not the optimal value of the evaluation value which is measured from the master, is determined using experiments, calculations, and the like in advance and strategy adjustment is performed so as to match the target value which is determined in this manner.
However, the determining of the target value where the evaluation value which is measured from the optical disc in this manner is optimized in advance is extremely difficult in practice in terms of the characteristics where the deviations which occur between the master and the optical disc in the manner described above.
Therefore, in order so that signal quality of the optical disc as a final product is appropriate in practice, it is realistic that the forming of the optical disc and the measuring of the evaluation value thereof is performed each time and strategy adjustment of the master is performed based on the result of measuring of the evaluation value of the optical disc.
For confirmation, a specific process of an adjustment method of a master strategy such as this will be described with reference to a flowchart of FIG. 8.
First, recording is performed with regard to a master (step S1) and an optical disc is created based on the master after recording (step S2).
After this, the measuring of the evaluation value with regard to the optical disc which has been created is performed (step S3) and whether or not the evaluation value is within a permissible range is identified (step S4).
Adjustment of a master strategy which is based on the result of measuring the evaluation value is performed as a strategy adjustment process in a case where the evaluation value is within a permissible range (step S5). Specifically, adjustment of the strategy, where the evaluation value which is measured in step S3 is an optimal value, is performed. After the strategy adjustment process such as this, the process is executed again from the master recording (step S1). That is, due to this, the adjustment of the strategy is repeated until the evaluation value which is measured from the optical disc is within the permissible range.
According to the method described above, it is possible to more reliably manufacture a high-quality optical disc by adjusting the master strategy based on the evaluation value which is measured from the optical disc.